1. Field Of The Invention:
The present invention pertains to an improvement in the keyboard arrangement of electronic musical instrument designed to generate desired expression sounds by a mere depression of keys.
2. Description Of The Prior Art:
Control of expression sounds or the so called "after-control" which is performed by the operation of keys of the keyboard of an electronic musical instrument is intended to impart variations of sound volume, tone color and tone pitch to the musical sounds generated from the tone source, in accordance with the magnitude of the depression force and speed of any desired key or keys, to thereby add subtle expression effects to the musical sounds, in accordance with the intension of the player himself or with the prescribed musical scores.
In a musical instrument such as a piano using strings, it is possible to produce delicate variations of sounds by varying the depression force and speed of a key. In an electronic musical instrument, however, only a predetermined simple sound corresponding to a certain note of a certain tone interval is produced by, for example, a low frequency oscillator circuit. With only such simple musical sounds, however it is impossible to perform a playing of delicate music, and the sounds produced would be only monotonous that would cause no musical sentiment to the listeners.
In order to overcome this drawback of the electronic musical instrument, there has been proposed to attach an independent expression generating means to each key of the electronic musical instrument to enable a desired expression or after-control effect to be added to the normal musical sounds. In the electronic musical instrument of the prior art, the addition of such an expression, i.e. after-control effect of tone color, tone volume and, for example, vibrato effect, to the basic musical sounds was carried out by independent control devices assigned exclusively for these purposes, and these devices were provided independently of the keyboard arrangement of the instrument. Therefore, the overall structure of the electronic musical instrument tended to become quite complicated and accordingly expensive. Besides, those who play a piano but have no experience in playing an electronic musical instrument will find this instrument quite difficult to operate. Therefore, there has been a demand for an electronic musical instrument which can produce various controlled effects in a much simpler manner without requiring such additional independent control devices.
In order to meet such a demand, there has been proposed an improved keyboard arrangement having a plurality of key-associated sensors each comprising a conductive elastic member capable of being compressed in accordance with a vertical and/or horizontal key movement to vary the impedance of the conductive member and to give off a control signal corresponding to the degree of such movement of the key. An electrical signal derived from the impedance variation of the conductive elastic member by the selective depression of keys is employed as an after-control signal.
An example of such known arrangement comprises a lengthy ribbon of conductive rubber-like member extending in the direction of the row of keys of the keyboard and beneath the row of keys. A depression of a key will compress and deform the conductive rubber-like member so that the electric resistance in said conductive member is varied, and such variation of resistance is derived as a control signal of the tone which is generated at the tone generator circuit.
In such arrangement, however, the material of the detecting member with which the speed and the amount of the key depression are detected is rubber or like elastic material. Accordingly, it is difficult to expect an identical property throughout the entire portions of such elastic material even when keys are depressed with an identical force or speed. Thus, there is the drawback that the generated sounds could have unintended different expressions for the respective keys. However, an effort to eliminate this drawback by seeking a conductive elastic material having an identical quality throughout thereof will be practically in vain and would lead to a high cost.